Thanks Gilles for pointing this discussion out. It appears that the use of
the MPI_DATATYPE_NULL in the example 5.23 is correct, the standard clearly
mentions the receiver datatype is only significant at the root.
George.
On Thu, Dec 8, 2022 at 7:03 PM Jim Edwards via mpi-comments <
mpi-comments(a)lists.mpi-forum.org> wrote:
> Right, so how do I formally request that the standard be updated to
> clarify this issue?
>
> On Thu, Dec 8, 2022 at 4:56 PM gilles--- via mpi-comments <
> mpi-comments(a)lists.mpi-forum.org> wrote:
>
>> I have a different recollection.
>>
>>
>>
>> The link is broken, here is one that works for me
>>
>> https://lists.mpi-forum.org/pipermail/mpi-forum/2016-January/003152.html
>>
>> TL;DR from Bill Gropp:
>>
>> "The standard says that the null handles are invalid for input unless explicitly permitted. There’s no exemption for a datatype argument where the associated count is zero."
>>
>>
>>
>> IIRC there was no objection to updating the standard in order to allow
>> this, but unless this has been completed, I am afraid MPI_DATATYPE_NULL is
>> not a valid datatype here
>>
>>
>>
>> Gilles
>>
>> ----- Original Message -----
>>
>> You are correct. The MPI_DATATYPE_NULL is an acceptable datatype for
>> cases where the target processor sends or receives no data. The standard
>> uses MPI_DATATYPE_NULL in 2 instances (in example 5.23) to highlight no
>> data movement, but fails to make a clear reference to the fact that this is
>> an acceptable use.
>>
>> George.
>>
>> On Thu, Dec 8, 2022 at 5:31 PM Jim Edwards via mpi-comments <
>> mpi-comments(a)lists.mpi-forum.org> wrote:
>>
>>> There seems to be some ambiguity in the standard with respect to usage
>>> of the MPI_DATATYPE_NULL variable.
>>> It would seem to me that if an MPI routine such as MPI_Send or
>>> MPI_ALLTOALLW has a data count argument of 0
>>> then MPI_DATATYPE_NULL should be an acceptable value for the datatype.
>>> Here is a discussion from several years
>>> ago with openmpi developers. It references a discussion in the
>>> standards forum but I can no longer find it.
>>>
>>> http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php
>>>
>>> Would it be possibly to clarify this case in the next iteration of the
>>> standard?
>>>
>>> --
>>> Jim Edwards
>>>
>>> CESM Software Engineer
>>> National Center for Atmospheric Research
>>> Boulder, CO
>>> _______________________________________________
>>> mpi-comments mailing list
>>> mpi-comments(a)lists.mpi-forum.org
>>> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments
>>
>>
>> _______________________________________________
>> mpi-comments mailing list
>> mpi-comments(a)lists.mpi-forum.org
>> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments
>>
>
>
> --
> Jim Edwards
>
> CESM Software Engineer
> National Center for Atmospheric Research
> Boulder, CO
> _______________________________________________
> mpi-comments mailing list
> mpi-comments(a)lists.mpi-forum.org
> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments
>
Right, so how do I formally request that the standard be updated to clarify
this issue?
On Thu, Dec 8, 2022 at 4:56 PM gilles--- via mpi-comments <
mpi-comments(a)lists.mpi-forum.org> wrote:
> I have a different recollection.
>
>
>
> The link is broken, here is one that works for me
>
> https://lists.mpi-forum.org/pipermail/mpi-forum/2016-January/003152.html
>
> TL;DR from Bill Gropp:
>
> "The standard says that the null handles are invalid for input unless explicitly permitted. There’s no exemption for a datatype argument where the associated count is zero."
>
>
>
> IIRC there was no objection to updating the standard in order to allow
> this, but unless this has been completed, I am afraid MPI_DATATYPE_NULL is
> not a valid datatype here
>
>
>
> Gilles
>
> ----- Original Message -----
>
> You are correct. The MPI_DATATYPE_NULL is an acceptable datatype for cases
> where the target processor sends or receives no data. The standard
> uses MPI_DATATYPE_NULL in 2 instances (in example 5.23) to highlight no
> data movement, but fails to make a clear reference to the fact that this is
> an acceptable use.
>
> George.
>
> On Thu, Dec 8, 2022 at 5:31 PM Jim Edwards via mpi-comments <
> mpi-comments(a)lists.mpi-forum.org> wrote:
>
>> There seems to be some ambiguity in the standard with respect to usage of
>> the MPI_DATATYPE_NULL variable.
>> It would seem to me that if an MPI routine such as MPI_Send or
>> MPI_ALLTOALLW has a data count argument of 0
>> then MPI_DATATYPE_NULL should be an acceptable value for the datatype.
>> Here is a discussion from several years
>> ago with openmpi developers. It references a discussion in the standards
>> forum but I can no longer find it.
>>
>> http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php
>>
>> Would it be possibly to clarify this case in the next iteration of the
>> standard?
>>
>> --
>> Jim Edwards
>>
>> CESM Software Engineer
>> National Center for Atmospheric Research
>> Boulder, CO
>> _______________________________________________
>> mpi-comments mailing list
>> mpi-comments(a)lists.mpi-forum.org
>> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments
>
>
> _______________________________________________
> mpi-comments mailing list
> mpi-comments(a)lists.mpi-forum.org
> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments
>
--
Jim Edwards
CESM Software Engineer
National Center for Atmospheric Research
Boulder, CO
I have a different recollection.
The link is broken, here is one that works for me
https://lists.mpi-forum.org/pipermail/mpi-forum/2016-January/003152.html
TL;DR from Bill Gropp:
"The standard says that the null handles are invalid for input unless
explicitly permitted. There’s no exemption for a datatype argument
where the associated count is zero."
IIRC there was no objection to updating the standard in order to allow
this, but unless this has been completed, I am afraid MPI_DATATYPE_NULL
is not a valid datatype here
Gilles
----- Original Message -----
You are correct. The MPI_DATATYPE_NULL is an acceptable datatype for
cases where the target processor sends or receives no data. The standard
uses MPI_DATATYPE_NULL in 2 instances (in example 5.23) to highlight no
data movement, but fails to make a clear reference to the fact that this
is an acceptable use.
George.
On Thu, Dec 8, 2022 at 5:31 PM Jim Edwards via mpi-comments <mpi-
comments(a)lists.mpi-forum.org> wrote:
There seems to be some ambiguity in the standard with respect to usage
of the MPI_DATATYPE_NULL variable.
It would seem to me that if an MPI routine such as MPI_Send or MPI_
ALLTOALLW has a data count argument of 0
then MPI_DATATYPE_NULL should be an acceptable value for the datatype.
Here is a discussion from several years
ago with openmpi developers. It references a discussion in the
standards forum but I can no longer find it.
http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php
Would it be possibly to clarify this case in the next iteration of the
standard?
--
Jim Edwards
CESM Software Engineer
National Center for Atmospheric Research
Boulder, CO
_______________________________________________
mpi-comments mailing list
mpi-comments(a)lists.mpi-forum.org
https://lists.mpi-forum.org/mailman/listinfo/mpi-comments
You are correct. The MPI_DATATYPE_NULL is an acceptable datatype for cases
where the target processor sends or receives no data. The standard
uses MPI_DATATYPE_NULL in 2 instances (in example 5.23) to highlight no
data movement, but fails to make a clear reference to the fact that this is
an acceptable use.
George.
On Thu, Dec 8, 2022 at 5:31 PM Jim Edwards via mpi-comments <
mpi-comments(a)lists.mpi-forum.org> wrote:
> There seems to be some ambiguity in the standard with respect to usage of
> the MPI_DATATYPE_NULL variable.
> It would seem to me that if an MPI routine such as MPI_Send or
> MPI_ALLTOALLW has a data count argument of 0
> then MPI_DATATYPE_NULL should be an acceptable value for the datatype.
> Here is a discussion from several years
> ago with openmpi developers. It references a discussion in the standards
> forum but I can no longer find it.
>
> http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php
>
> Would it be possibly to clarify this case in the next iteration of the
> standard?
>
>
> --
> Jim Edwards
>
> CESM Software Engineer
> National Center for Atmospheric Research
> Boulder, CO
> _______________________________________________
> mpi-comments mailing list
> mpi-comments(a)lists.mpi-forum.org
> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments
>
There seems to be some ambiguity in the standard with respect to usage of
the MPI_DATATYPE_NULL variable.
It would seem to me that if an MPI routine such as MPI_Send or
MPI_ALLTOALLW has a data count argument of 0
then MPI_DATATYPE_NULL should be an acceptable value for the datatype.
Here is a discussion from several years
ago with openmpi developers. It references a discussion in the standards
forum but I can no longer find it.
http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php
Would it be possibly to clarify this case in the next iteration of the
standard?
--
Jim Edwards
CESM Software Engineer
National Center for Atmospheric Research
Boulder, CO
